Apparatus and method for generating an electromagnetic radiation

ABSTRACT

A method for generating an electromagnetic radiation includes the following operations. A target material is introduced in a chamber. A light beam is irradiated on the target material in the chamber to generate plasma and an electromagnetic radiation. The electromagnetic radiation is collected with an optical device. A gas mixture is introduced in the chamber. The gas mixture includes a first buffer gas reactive to the target material, and a second buffer gas to slow down debris of the target material and/or plasma by-product, so as to increase an reaction efficiency of the target material and the first buffer gas, and to reduce deposition of the debris of the target material and/or the plasma by-product on the optical device.

BACKGROUND

Extreme-ultraviolet (EUV) light is an electromagnetic radiation, e.g.,having a wavelength range lower than about 100 nanometers or less. EUVlight has been used in photolithography operation as an exposure lightsource to fabricate extremely small features.

The EUV light can be formed along with plasma by irradiating a targetmaterial with a laser beam, and the generated EUV light is thencollected and transmitted to an exposure system by an optical device.During generation of the plasma and EUV light, however, debris of thetarget material and plasma by-product such as ions of the targetmaterial tend to deposit on the optical device, thereby damaging theoptical device and deteriorating its optical performance.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the embodiments of the present disclosure are best understoodfrom the following detailed description when read with the accompanyingfigures. It is noted that, in accordance with the standard practice inthe industry, various structures are not drawn to scale. In fact, thedimensions of the various structures may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 is a flow chart illustrating a method for generating anelectromagnetic radiation according to various aspects of one or moreembodiments of the present disclosure.

FIG. 2 is a schematic diagram illustrating an apparatus in accordancewith some embodiments of the present disclosure.

FIG. 2A is a schematic top view of an optical device in accordance withsome embodiments of the present disclosure.

FIG. 2B is a schematic cross-sectional view of an optical device inaccordance with some embodiments of the present disclosure.

FIG. 3 is a schematic top view of an optical device in accordance withsome embodiments of the present disclosure.

FIG. 4 shows an EUV spectrum excited by a light beam in accordance withsome embodiments of the present disclosure.

FIG. 5 is a schematic diagram illustrating an apparatus in accordancewith some embodiments of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of elements and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below.” “lower,”“above,” “over,” “upper.” “on,” and the like, may be used herein forease of description to describe one element or feature's relationship toanother element(s) or feature(s) as illustrated in the figures. Thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. The apparatus may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein may likewise be interpretedaccordingly.

As used herein, the terms such as “first.” “second” and “third” describevarious elements, components, regions, layers and/or sections, theseelements, components, regions, layers and/or sections should not belimited by these terms. These terms may be only used to distinguish oneelement, component, region, layer or section from another. The termssuch as “first.” “second” and “third” when used herein do not imply asequence or order unless clearly indicated by the context.

As used herein, the terms “approximately,” “substantially,”“substantial” and “about” are used to describe and account for smallvariations. When used in conjunction with an event or circumstance, theterms can refer to instances in which the event or circumstance occursprecisely as well as instances in which the event or circumstance occursto a close approximation. For example, when used in conjunction with anumerical value, the terms can refer to a range of variation of lessthan or equal to ±10% of that numerical value, such as less than orequal to ±5%, less than or equal to ±4%, less than or equal to ±3%, lessthan or equal to ±2%, less than or equal to ±1%, less than or equal to±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. Forexample, two numerical values can be deemed to be “substantially” thesame or equal if a difference between the values is less than or equalto ±10% of an average of the values, such as less than or equal to ±5%,less than or equal to ±4%, less than or equal to ±3%, less than or equalto ±2%, less than or equal to ±1%, less than or equal to ±0.5%, lessthan or equal to +0.1%, or less than or equal to ±0.05%. For example,“substantially” parallel can refer to a range of angular variationrelative to 0° that is less than or equal to ±10°, such as less than orequal to ±5°, less than or equal to ±40, less than or equal to ±3°, lessthan or equal to ±2°, less than or equal to ±10, less than or equal to±0.50, less than or equal to ±0.10, or less than or equal to ±0.050. Forexample, “substantially” perpendicular can refer to a range of angularvariation relative to 90° that is less than or equal to ±10, such asless than or equal to ±50, less than or equal to ±4°, less than or equalto ±30, less than or equal to ±2°, less than or equal to ±10, less thanor equal to ±0.5°, less than or equal to ±0.10, or less than or equal to+0.050.

The advanced lithography process, method, and materials described in thecurrent disclosure can be used in many applications, including fin-typefield effect transistors (FinFETs). For example, the fins may bepatterned to produce a relatively close spacing between features, forwhich the above disclosure is well suited. In addition, spacers used informing fins of FinFETs can be processed according to the abovedisclosure.

In one or more embodiments of the present disclosure, a method and anapparatus for generating an electromagnetic radiation such as EUV lightis provided. The method includes introducing a gas mixture into thechamber during operation of generating the EUV light. The gas mixtureincludes a first buffer gas and a second buffer gas. The first buffergas is configured to react with a target material to form a gaseousproduct, which can be exhausted from the chamber to reduce deposition ofthe debris on an optical device and/or on the inner wall of the chamber.The second buffer gas having a larger molecular mass, gas density andviscosity than that of the first buffer gas, and is configured to helpslow down debris of the target material and/or plasma by-product, so asto increase the reaction efficiency of the target material and the firstbuffer gas, and to reduce deposition of the target material and/orplasma by-product. The second buffer gas can also be excited to emit anEUV light, and thus can also help to increase the amount of EUV light.

FIG. 1 is a flow chart illustrating a method for generating anelectromagnetic radiation according to various aspects of one or moreembodiments of the present disclosure. The method 100 begins withoperation 110 in which a target material is introduced in a chamber. Themethod 100 proceeds with operation 120 in which a light beam isirradiated on the target material in the chamber to generate plasma andan electromagnetic radiation. The method 100 proceeds with operation 130in which the electromagnetic radiation is collected with an opticaldevice. The method 100 proceeds with operation 140 in which a gasmixture is introduced in the chamber. The gas mixture includes a firstbuffer gas reactive to the target material, and a second buffer gas toslow down debris of the target material and/or plasma by-product, so asto increase an reaction efficiency of the target material and the firstbuffer gas, and to alleviate deposition of the debris of the targetmaterial and/or the plasma by-product on the optical device.

The method 100 is merely an example, and is not intended to limit thepresent disclosure beyond what is explicitly recited in the claims.Additional operations can be provided before, during, and after themethod 100, and some operations described can be replaced, eliminated,or moved around for additional embodiments of the method.

FIG. 2 is a schematic diagram illustrating an apparatus in accordancewith some embodiments of the present disclosure. As shown in FIG. 2, theapparatus 1 for generating an electromagnetic radiation 16 includes achamber 10, a target material supplier 20, a light source system 30, anoptical device 40 and a buffer gas supplier 50. In some embodiments, theapparatus 1 is designed to generate an electromagnetic radiation 16 suchas an extreme-ultraviolet (EUV) light (also referred to as soft x-rays),having a wavelength range lower than about 100 nanometers, but is notnecessarily limited thereto. By way of example, an EUV light having awavelength of about 13.5 nm can be generated. During operation, thechamber 10 may be maintained at a low-pressure state or vacuum state.

The target material supplier 20 is connected to the chamber 10 andconfigured to supply a target material 22 to the chamber 10. The targetmaterial 22 may be selected based on the wavelength of the EUV light tobe generated. For example, the target material 22 may include tin, andthe EUV light having a wavelength of about 13.5 nm can be generated. Insome other embodiments, lithium or other suitable target material can beselected to generate an EUV light having a different wavelength. Thetarget material 22 may be introduced to the chamber 10 in the form of adroplet, a stream, a cluster or the like.

The light source system 30 is configured to emit a light beam L on thetarget material 22. The target material 22 can be excited by the lightbeam L, and converted into a plasma state, with generation ofelectromagnetic radiation 16 within EUV wavelength range. In someembodiments, the light beam L may include a pulse light. In someembodiments, the light source system 30 may include a laser sourcesystem 30 configured to emit a laser beam. The laser beam may include,for example. CO₂ laser or the like. The wavelength of CO₂ laser may bewithin a middle infra-red wavelength range, e.g., within the range ofabout 9 micrometers to about 11 micrometers. CO₂ laser may producerelatively high conversion efficiency on some target material such astin.

The electromagnetic radiation 16 is generated during de-excitation andrecombination of ions emitted from the plasma. The optical device 40 isdisposed in the chamber 10 and configured to collect the electromagneticradiation 16. In some embodiments, the optical device 40 can collect anddirect the electromagnetic radiation 16 toward an exposure light sourcesystem in a photolithography apparatus. In some embodiments, the opticaldevice 40 may include a reflector mirror, which can reflect theelectromagnetic radiation 16, and focus the electromagnetic radiation 16to a focus point. By way of example, the optical device 40 may include amulti-layer mirror (MLM) capable of reflecting EUV light within adesignated wavelength range.

In some embodiments, the buffer gas supplier 50 includes a gas outlet 54connected to a first side 101 of the chamber 10, and the gas mixture 52is introduced to the chamber 10 from the first side 101. The lightsource system 30 may be disposed on the first side 101 of the chamber10, and the light beam L may be emitted to the chamber 10 from the firstside 101. In some embodiments, the optical device 40 is disposed nearthe first side 101 of the chamber 10, and the light beam L can beemitted to the chamber 10 through an aperture 42 of the optical device40. The gas outlet 54 of the buffer gas supplier 50 is in communicationwith the aperture 42 of the optical device 40, and the gas mixture 52 isblown to the chamber 101 through the aperture 42 of the optical device40. In some embodiments, the target material supplier 20 is connected toa second side 102 of the chamber 10, and configured to supply the targetmaterial 22 to the chamber 10 from the second side 102. As shown in FIG.2, the target material supplier 20 may supply the target material 22 toan irradiation region 14 in the chamber 10 from the second side 102,while the light source system 30 may emit the light beam L to theirradiation region 14 from the first side 101. In the irradiation region14, the target material 22 is excited by the light beam L, generatingplasma and EUV light.

In addition to generating the electromagnetic radiation 16 such as EUVlight, undesirable plasma by-products also appear in the chamber 10. Forexample, the plasma by-products such as target material vapor mayinclude neutral atoms and ions of the target material 22 when generatingthe EUV light. Also, debris of the target material 22 i.e., the targetmaterial 22 not excited by the light beam L would also appear in thechamber 10 when generating the EUV light. The debris, atoms and ions ofthe target material 22 tend to travel toward the optical device 40, andwould deposit on the optical device 40 or the inner wall of the chamberwhen generating the EUV light. The debris, atoms and ions of the targetmaterial 22 deposited on the optical device 40 deteriorate the opticalperformance such as reflectivity of the optical device 40, andpotentially damage the optical device 40. Particularly, the ions of thetarget material 22 having higher velocity and kinetic energy than theatoms of the target material 22, would seriously deteriorate the opticalperformance of the optical device 40, thereby reducing the efficiency ofEUV light generation. In some embodiments, the apparatus 1 may furtherinclude a target material catcher 24 connected to the chamber 10, andconfigured to catch the remaining target material 22. The targetmaterial catcher 24, for example, may be connected to a third side 103opposing to the first side 101 where the target material supplier 20 isdisposed, so as to catch the remaining target material 22.

In view of the problems caused by plasma by-product and debris of thetarget material 22, a buffer gas supplier 50 is incorporated in thechamber 10. The buffer gas supplier 50 is connected to the chamber 10and configured to introduce a gas mixture 52 to the chamber 10. The gasmixture 52 may include a first buffer gas reactive to the targetmaterial 22, and a second buffer gas configured to slow down debris ofthe target material 22 and/or plasma by-product. The first buffer gascan react with the debris of the target material 22, and produce agaseous product. The gaseous product can be easily exhausted from thechamber 10 through one or more exhaust outlets 58, and thus the debrisof the target material 22 can be reduced. In some embodiments, a pump(not shown) may be used to pump the gaseous product out of the chamber10. In some embodiments, the target material 22 includes tin (Sn), andthe first buffer gas includes hydrogen gas (H₂). Hydrogen gas is able toreact with tin, forming gaseous tin hydride (SnH₄). The gaseous tinhydride can be exhausted from the chamber 10 by, e.g., a pump, such thatthe amount of tin debris can be reduced.

Refer to Table 1. Table 1 lists velocity and kinetic of neutral atomsand ions of tin during generating the EUV light in accordance with someembodiments of the present disclosure.

TABLE 1 Plasma by- Velocity Kinetic energy product (Km/s) (KeV) Ions10-100  0.06-6 Neutral atoms 6-40 0.015-1

As listed in Table 1, the neutral atoms and ions of tin have highvelocity and kinetic energy in the chamber 10. At such a high velocity,the reaction of the first buffer gas and the neutral atoms/ions of thetarget material 22 is less effective.

The second buffer gas is introduced in the chamber 10 to slow downdebris of the target material 12 and/or plasma by-product. In someembodiments, the molecular mass of the second buffer gas is larger thanthat of the first buffer gas, so as to generate. In some embodiments,the gas density of the second buffer gas is larger than that of thefirst buffer gas. In some embodiments, the viscosity of the secondbuffer gas is larger than that of the first buffer gas. The secondbuffer gas may include a noble gas, which does not react with the targetmaterial 22. By way of example, the second buffer gas may include xenongas, argon gas, krypton gas, neon gas or a combination thereof.

Refer to Table 2. Table 2 lists molecular mass, gas density andviscosity of the first buffer gas (hydrogen gas), the target material(tin) and the second buffer gas (xenon) in accordance with someembodiments of the present disclosure.

TABLE 2 Molar Gas density Absolute mass (g/L)@STP Viscosity H₂ 2.010.089 0.88 (10⁻⁵ Pa · s at 20° C.) Sn 118.71 5.299 — Xe 131.29 5.8942.28 (10⁻⁵ Pa · s at 20° C.) Ar 39.95 1.783 2.23 (10⁻⁵ Pa · s at 20° C.)Ne 20.18 0.90 3.13 (10⁻⁵ Pa · s at 20° C.) Kr 83.80 3.749 2.53 (10⁻⁵ Pa· s at 25° C.)

As shown in Table 2, noble gas such as xenon gas (Xe), argon gas (Ar),krypton gas (Kr) or neon gas (Ne) has larger molecular mass thanhydrogen gas (H₂), and thus has higher momentum than hydrogen gas whencolliding tin. The larger molecular mass of the above noble gas alsogenerates larger drag force than hydrogen gas Accordingly, noble gassuch as xenon has better stopping effect on tin than hydrogen gas. Noblegas such as xenon gas has larger gas density than hydrogen gas, and thusthe possibility of collision between xenon gas and tin is higher. Also,noble gas such as xenon has larger viscosity than than hydrogen gas(H₂), and thus is more effective in slowing down tin than hydrogen gas.

A theoretic drag force of an object in a fluid can be obtained by meansof a drag equation: F_(D)=½ρvC_(D)A,

where F_(D) is the drag force;

ρ is the density of the fluid;

v is the velocity of the object relative to the fluid;

C_(D) is a drag coefficient; and

A is the cross-sectional area.

As shown in Table 2, since the gas density of the second buffer gas islarger than that of the first buffer gas, the second buffer gas canprovide a larger drag force on the target material 22 than the firstbuffer gas. For example, the drag force provided by xenon gas is about66.2 times the drag force provided by hydrogen gas. Accordingly, thesecond buffer gas can help to slow down the the high-speed andhigh-energy ions and atoms of tin during generation of EUV light. As aresult, hydrogen gas can react with tin more efficiently, and depositionof the debris of tin and/or neutral atoms and ions of tin on the opticaldevice can be reduced. In some embodiments, the second buffer gas canfurther help to carry the debris of tin and/or neutral atoms and ions oftin away from the optical device 40 as shown by arrows A, such thatdeposition of the debris of tin and/or neutral atoms and ions of tin onthe optical device can be reduced.

Refer to FIG. 2, FIG. 2A and FIG. 2B. FIG. 2A is a schematic top view ofan optical device in accordance with some embodiments of the presentdisclosure, and FIG. 2B is a schematic cross-sectional view of anoptical device in accordance with some embodiments of the presentdisclosure. As shown in FIG. 2. FIG. 2A and FIG. 2B, the optical device40 may include a reflector mirror, which can reflect the electromagneticradiation 16, and focus the electromagnetic radiation 16 to a focuspoint. By way of example, the optical device 40 may include amulti-layer mirror (MLM) capable of reflecting EUV light within adesignated wavelength range. In some embodiments, the optical device 40may include an aperture 42 having a first sub-aperture 421 and a secondsub-aperture 422. The first sub-aperture 421 may be disposed at anoriginal point of the reflector mirror, and the light beam L can emit tothe chamber 10 through the first sub-aperture 421, exciting the targetmaterial 22. The second sub-aperture 422 may be disposed adjacent to thefirst sub-aperture 421, and the gas mixture 52 may be introduced intothe chamber 10 through the second sub-aperture 422. In some embodiments,the second sub-aperture 42 may have an annular shape surrounding thefirst sub-aperture 421, such that the gas mixture 52 can be introducedinto the chamber 10 more uniformly. In some embodiments, the firstsub-aperture 421 and the second sub-aperture 422 may be divided by abaffle 44. In some other embodiments, the first sub-aperture 421 and thesecond sub-aperture 422 may be connected to each other. The baffle 44may be configured to direct the flow of the gas mixture 52 to increasethe ability of retarding the debris of the target material and/or theplasma by-product. For example, the baffle 44 may include an inclinededge extending outwardly, such that the flow of the gas mixture 52 canbe directed outwardly. In some embodiments, the gas mixture 52 canprovide a gas curtain over the optical device 40, preventing the debrisof the target material and/or the plasma by-product from falling on thesurface of the optical device 40. The baffle 44 may also be configuredto reduce the cross-sectional area of the second sub-aperture 422 toincrease the velocity of the gas mixture 52 when entering the chamber10.

Refer to FIG. 3. FIG. 3 is a schematic top view of an optical device inaccordance with some embodiments of the present disclosure. As shown inFIG. 3, in some other embodiments, the optical device 40 may include anaperture 42 having a first sub-aperture 421, a second sub-aperture 422and a third sub-aperture 423. The first sub-aperture 421, the secondsub-aperture 422 and the third sub-aperture 423 may be configured toallow light beam and different gases passing, respectively. In someembodiments, the light beam L can emit to the chamber 10 through thefirst sub-aperture 421. The second sub-aperture 422 and the thirdsub-aperture 423 may be arranged adjacent to the first sub-aperture 421in the radial direction, and configured to introduce different gases. Byway of example, the first buffer gas may be introduced through thesecond sub-aperture 422, and the second buffer gas may be introducedthrough the third sub-aperture 423, or vice versa.

Refer to FIG. 4. FIG. 4 shows an EUV spectrum excited by a light beam inaccordance with some embodiments of the present disclosure. As shown inFIG. 4, tin, can be used as a target material and excited by a lightbeam such as a CO₂ laser beam to generate an EUV light having awavelength of about 13.5 nm. The EUV light having a wavelength of about13.5 nm can be delivered to an exposure light source system in aphotolithography apparatus. In some embodiments, xenon gas is used as abuffer gas and introduced to slow down debris of the target materialand/or plasma by-product. Xenon gas, however, can also be excited by thelight beam to generate an EUV light. The EUV light generated by xenongas may have a wavelength range with two peaks, where one of the peakshas a wavelength of about 13.5 nm. Thus, using xenon gas as the buffergas not only can help to slow down debris of the target material and/orplasma by-product, but also can help to increase the amount of EUVlight.

The amount the first buffer gas and the second buffer gas can bemodified based on different considerations. For example, the amount ofthe first buffer gas can be increased to enhance the reaction betweenthe first buffer gas and the target material. The amount of the secondbuffer gas can be increase to enhance its ability to slow down theplasma by-product, and to increase the amount of EUV light. In someembodiments, the amount ratio of the second buffer gas to the firstbuffer gas is less than 1, but is not necessarily limited thereto. Byway of example, the amount ratio of the second buffer gas to the firstbuffer gas is ranging from about 0.0001% to about 50%, ranging fromabout 0.001% to about 50%, ranging from about 0.01% to about 50%,ranging from about 0.1% to about 50%, ranging from about 1% to about50%, or ranging from about 5% to about 50%, ranging from about 10% toabout 50%, but is not limited thereto.

The apparatus for generating an electromagnetic radiation is not limitedto the above-mentioned embodiments, and may have other differentembodiments. To simplify the description and for the convenience ofcomparison between each of the embodiments of the present disclosure,the identical components in each of the following embodiments are markedwith identical numerals. For making it easier to compare the differencebetween the embodiments, the following description will detail thedissimilarities among different embodiments and the identical featureswill not be redundantly described.

FIG. 5 is a schematic diagram illustrating an apparatus in accordancewith some embodiments of the present disclosure. As shown in FIG. 5, theapparatus 2 for generating an electromagnetic radiation 16 includes achamber 10, a target material supplier 20, a light source system 30, anoptical device 40, a buffer gas supplier 50 and a recycle system 60. Theapparatus 2 may be designed to generate an electromagnetic radiationsuch as an EUV light. By way of example, an EUV light having awavelength of about 13.5 nm can be generated.

The target material supplier 20 is connected to the chamber 10 andconfigured to supply a target material 22 to the chamber 10. The targetmaterial 22 may include tin, and the EUV light having a wavelength ofabout 13.5 nm can be generated. The target material 22 may be introducedto the chamber 10 in the form of a droplet, a stream, a cluster or thelike.

The light source system 30 is configured to emit a light beam L on thetarget material 22. The target material 22 can be excited by the lightbeam L, thereby being converted into a plasma state, withelectromagnetic radiation 16 within EUV wavelength range. In someembodiments, the light beam L may include a pulse light. In someembodiments, the light source system 30 may include a laser sourcesystem 30 configured to emit a laser beam. The laser beam may include,for example, CO₂ laser or the like. The wavelength of CO₂ laser may bewithin a middle infra-red wavelength range. e.g., within the range ofabout 9 micrometers to about 11 micrometers. CO₂ laser may produce arelatively high conversion efficiency on some target material such astin.

The optical device 40 is disposed in the chamber 10 and configured tocollect the electromagnetic radiation 16. In some embodiments, theoptical device 40 can collect and direct the electromagnetic radiation16 toward an exposure light source system in a photolithographyapparatus. In some embodiments, the optical device 40 may include areflector mirror such as a multi-layer mirror (MLM) capable ofreflecting EUV light within a designated wavelength range. The buffergas supplier 50 is connected to the chamber 10 and configured tointroduce a gas mixture 52 to an irradiation region 14 in the chamber10. In some embodiments, the apparatus 2 may further include a targetmaterial catcher 24 connected to the chamber 10, and configured to catchthe remaining target material 22.

The recycle system 60 is connected to the chamber 10 through an exhaustoutlet 58 for example, and connected to the buffer gas supplier 50, andconfigured to recycle the gas mixture 52. In some embodiments, therecycle system 60 includes a filtration unit 62 such as a membranefiltration unit to filter the debris of the target material 22. In someembodiments, a flow control component 64 such as a valve may beinstalled in the recycle system 60 to control the flow of gas mixture52. The gas mixture 52 may be recycled and delivered to the buffer gassupplier 50 for reuse. In some embodiments, the first buffer gas such ashydrogen gas can be filtered, while the second buffer gas such as xenongas is recycled.

In some embodiments of the present disclosure, an apparatus forgenerating an electromagnetic radiation such as EUV light is provided.The apparatus includes a buffer gas supplier for introducing a gasmixture into the chamber during operation of generating the EUV light.The gas mixture includes a first buffer gas and a second buffer gas. Thefirst buffer gas is configured to react with a target material to form agaseous product, which can be exhausted from the chamber to reducedeposition of the debris on an optical device and/or on the inner wallof the chamber. The second buffer gas having a larger molecular mass,gas density and viscosity than that of the first buffer gas, and isconfigured to help slow down debris of the target material and/or plasmaby-product, so as to increase the reaction efficiency of the targetmaterial and the first buffer gas, and to reduce deposition of thetarget material and/or plasma by-product. The second buffer gas can alsobe excited to emit an EUV light, and thus can also help to increase theamount of EUV light.

In some embodiments, a method for generating an electromagneticradiation includes the following operations. A target material isintroduced in a chamber. A light beam is irradiated on the targetmaterial in the chamber to generate plasma and an electromagneticradiation. The electromagnetic radiation is collected with an opticaldevice. A gas mixture is introduced in the chamber. The gas mixtureincludes a first buffer gas reactive to the target material, and asecond buffer gas to slow down debris of the target material and/orplasma by-product, so as to increase an reaction efficiency of thetarget material and the first buffer gas, and to reduce deposition ofthe debris of the target material and/or the plasma by-product on theoptical device.

In some embodiments, an apparatus includes a chamber, a target materialsupplier, a light source system, an optical device and a buffer gassupplier. The target material supplier is connected to the chamber andconfigured to supply a target material to the chamber. The light sourcesystem is configured to emit a light beam on the target material in thechamber to generate plasma and an electromagnetic radiation. The opticaldevice is disposed in the chamber and configured to collect theelectromagnetic radiation. The buffer gas supplier connected to thechamber and configured to introduce a gas mixture to the chamber. Thegas mixture includes a first buffer gas reactive to the target material,and a second buffer gas configured to slow down debris of the targetmaterial and/or plasma by-product.

In some embodiments, an apparatus includes a chamber, a target materialsupplier, a light source system, an optical device and a buffer gassupplier. The target material supplier is configured to supply a targetmaterial to the chamber. The light source system is configured to emit alight beam on the target material in the chamber to generate plasma andan electromagnetic radiation. The optical device is disposed in thechamber and configured to collect the electromagnetic radiation, whereinthe optical device includes an aperture. The buffer gas supplier isconnected to the chamber and configured to blow a gas mixture throughthe aperture of the optical device. The gas mixture includes a firstbuffer gas reactive to the target material, and a second buffer gashaving a molecular mass larger than that of the target material to carrydown debris of the target material and/or plasma by-product away fromthe optical device.

The foregoing outlines structures of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for generating an electromagneticradiation, comprising: introducing a target material in a chamber;irradiating a light beam on the target material in the chamber togenerate plasma and an electromagnetic radiation; collecting theelectromagnetic radiation with an optical device; and introducing a gasmixture in the chamber through a gas outlet in communication with anaperture of the optical device, wherein the gas outlet extends into theoptical device through the aperture, the gas mixture comprises a firstbuffer gas reactive to the target material, and a second buffer gas toslow down debris of the target material and/or plasma by-product, so asto increase an reaction efficiency of the target material and the firstbuffer gas, and to reduce deposition of the debris of the targetmaterial and/or the plasma by-product on the optical device, the firstbuffer gas comprises hydrogen gas, the second buffer gas comprises xenongas, and an amount ratio of the second buffer gas to the first buffergas is less than
 1. 2. The method of claim 1, wherein the gas mixture isintroduced in the chamber through the aperture of the optical device. 3.The method of claim 1, wherein a molecular mass of the second buffer gasis larger than that of the first buffer gas and that of the targetmaterial.
 4. The method of claim 1, wherein the target material includestin.
 5. An apparatus, comprising: a chamber; a target material supplierconnected to the chamber and configured to supply a target material tothe chamber; a light source system configured to emit a light beam onthe target material in the chamber to generate plasma and anelectromagnetic radiation; an optical device in the chamber andconfigured to collect the electromagnetic radiation, wherein the opticaldevice comprises an aperture; and a buffer gas supplier connected to thechamber and configured to introduce a gas mixture to the chamber,wherein the buffer gas supplier comprises a gas outlet extended into theoptical device through the aperture, the gas mixture comprises a firstbuffer gas reactive to the target material, and a second buffer gasconfigured to slow down debris of the target material and/or plasmaby-product.
 6. The apparatus of claim 5, wherein the gas outlet isconnected to a first side of the chamber, and the gas mixture isintroduced to the chamber from the first side.
 7. The apparatus of claim6, wherein the light source system is disposed on the first side of thechamber, and the light beam is emitted to the chamber from the firstside.
 8. The apparatus of claim 7, wherein the optical device isdisposed near the first side of the chamber, and the light beam isemitted to the chamber through the aperture of the optical device. 9.The apparatus of claim 8, wherein the gas outlet of the buffer gassupplier is in communication with the aperture of the optical device,and the gas mixture is introduced to the chamber through the aperture ofthe optical device.
 10. The apparatus of claim 6, wherein the targetmaterial supplier is connected to a second side of the chamber, andconfigured to supply the target material to the chamber from the secondside.
 11. The apparatus of claim 5, wherein a molecular mass of thesecond buffer gas is larger than that of the first buffer gas.
 12. Theapparatus of claim 5, wherein a gas density of the second buffer gas islarger than that of the first buffer gas.
 13. The apparatus of claim 5,wherein a viscosity of the second buffer gas is larger than that of thefirst buffer gas.
 14. The apparatus of claim 5, wherein the first buffergas includes hydrogen gas.
 15. The apparatus of claim 5, wherein thesecond buffer gas includes a noble gas.
 16. The apparatus of claim 15,wherein the second buffer gas includes xenon gas, argon gas, kryptongas, neon gas or a combination thereof.
 17. The apparatus of claim 5,further comprising a recycle system connected to the chamber and thebuffer gas supplier, and configured to recycle the gas mixture.
 18. Anapparatus, comprising: a chamber; a target material supplier configuredto supply a target material to the chamber; a light source systemconfigured to emit a light beam on the target material in the chamber togenerate plasma and an electromagnetic radiation; an optical device inthe chamber and configured to collect the electromagnetic radiation,wherein the optical device includes an aperture; and a buffer gassupplier connected to the chamber and configured to blow a gas mixturethrough the aperture of the optical device, wherein the buffer gassupplier comprises a gas outlet extended into the optical device throughthe aperture, the gas mixture comprises a first buffer gas reactive tothe target material, and a second buffer gas having a molecular masslarger than that of the target material to carry down debris of thetarget material and/or plasma by-product away from the optical device.19. The apparatus of claim 18, wherein the molecular mass of the secondbuffer gas is larger than that of the first buffer gas, a gas density ofthe second buffer gas is larger than that of the first buffer gas, and aviscosity of the second buffer gas is larger than that of the firstbuffer gas.
 20. The apparatus of claim 19, wherein the first buffer gasincludes hydrogen gas, and the second buffer gas includes xenon gas,argon gas, krypton gas, neon gas or a combination thereof.